Re: [Xen-devel] where is writable page table implemented?

[weiming <zephyr.zhao@xxxxxxxxx>]

Hi Tim,

Do you know under which situation we use writable page table instead of calling update_va_mapping? 

And do you know the purpose of the counter defined in page_info.u.in_use.type_info?
I understand that xen needs to keep track of the type of each page (L1_page_table_page, L2_page_table_page, pinned, unpinned, validated, etc), but why do we need to use the lower 26 bits of "type_info" as a counter? (in "get_page_type()", the counter is increased. )  Similarly,  get_page() / put_page() also increases/decreases the page.count_info. Could you please give me some hint about the usage of such counters?

Thanks a lot!
Weiming

On Tue, Apr 1, 2008 at 4:38 AM, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:

At 19:43 -0400 on 30 Mar (1206906207), weiming wrote:
> with writable page table, why guest os still calls update_va_mapping to
> update the pte?

It's faster to call into Xen with an explicit modification, or a list of
them, than to have xen trap and do a full x86 instruction emaulation to
figure out what you werere doing.

Cheers,

Tim.

--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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